Technical Abstract:
Longan (Dimocarpus longan L.) is an exotic tropical fruit native of Southwest Asia which belongs to the Sapindanceae family. In Puerto Rico, it was introduced in 1926 by USDA, Tropical Agriculture Research Station. In 1999 experimental plots were established for evaluation in various agroenvironments as a potential cash crop. There is very limited information on longan diseases which impinges on orchard management and fruit handling after harvest. During August to September, 2008 and April to May, 2009 disease-affected plant tissue was collected from longan trees at commercial farms and research orchards located at the western region of island. Tissue was superficially disinfected and transferred to acidified potato dextrose agar (APDA) to promote the development of fungi associated with injuries. A total of 30 fungal isolates were obtained from the examined tissue. Fungal isolates were characterized morphologically and molecularly by amplification of the rDNA ITS region. Several fungal species were identified: Albonectria rigidiuscula, Alternaria alternata, Botryosphaeria parva, B. rhodina, B. ribis, Fusarium chlamydosporum, F. culmorum, Phoma spp., Phomopsis spp. and Xylaria spp. The following fungi were pathogenic to longan inflorescences: Albonectria rigidiuscula, B. rhodina, F. culmorum, Pestalotiopsis spp. and Phoma spp. Higher disease severity was caused by B. rhodina, eight days after inoculation in inflorescences. Albonectria rigidiuscula and Phoma spp.caused rachis wilt and fruit mummification. Botryosphaeria rhodina and Pestalotiopsis sp. were pathogenic to fruit, colonizing 100% of longan fruit three days after inoculation.